(1) During the next year we will begin studies to determine if monoclonal anti-p15E can be used to prevent or slow the growth of intraperitoneally or subcutaneously injected tumor cells or to prolong the survival of tumor-bearing animals. Three hybridoma cell lines producing monoclonal antibodies to different epitopes on retroviral p15E are currently being used to produce sufficiently large quantities of antibodies from the culture supernatants for these experiments. Mice will be treated with either intact IgG or the F(ab')2 fragments of the antibodies. Control micewill be injected with the same amounts of purified IgG of F(ab')2 fragments of the same isotype as the monoclonal anti-p15E used. The antibodies will be used singularly and in various combinations. Mice will be injected prior to and at regular intervals after tumor cell inoculation. Circulating levels of anti-p15E and, if possible, p15E itself will be monitored during the course of the experiments. (2) We will continue our studies to determine circulating p15E levels in tumor-bearing mice and whether the levels of p15E correlate with tumor growth or metastasis. We will continue to use our competition ELISA assay to make these determinations, but during the next year we will attempt to determine what our lowest level of sensitivity will be using this assay. This will be done by injecting mice intravenously with predetermined amounts of p15E and obtaining blood samples for p15E determinations at very short intervals thereafter. (3) We will continue our studies aimed at determining whether the envelope glycoproteins of human T-cell leukemia-lymphoma virus (HTLV) react with anti-p15E antibodies. Using our rabbit anti-p15E, which reacts with HTLV proteins, we will attempt to affinity-purify the reactive material from HTLV preparations and to further identify it by SDS-PAGE and two-dimensional electrophoresis. If sufficient amounts of this p15E-reactive HTLV protein are obtained it will be sequenced and its sequence compared to the published sequences of the HTLV structural proteins. (IS)